This invention relates generally to a method for interconnecting and manufacturing tubular drill string components. More particularly, this invention relates to a method for angularly aligning adjacent tubular drill string components such as formation evaluation tools or drill collars.
Deep wells of the type commonly used for petroleum or geothermal exploration are typically less than 30 cm (12 inches) in diameter and on the order of 2 km (1.5 miles) long. These wells are drilled using drill strings assembled from relatively light sections (either 30 or 45 feet long) of steel drill pipe that are connected end-to-end by tool joints, additional sections being added to the uphole end as the hole deepens. The downhole end of the drill string typically includes a drill collar, formation evaluation tools and a dead weight section assembled from relatively heavy lengths of uniform diameter steel tubes ("drill collars") having an overall length on the order of 300 meters (1000 feet). A drill bit is attached to the downhole end of the lowermost drill collar, the weight of the collar causing the bit to bite into the earth. The drill string is either rotated from the surface to turn the bit, or a downhole mud motor or turbine is used to turn the bit while the drill string is fixed (i.e., not rotating). Drilling mud or air is pumped from the surface to the drill bit through an axial hole in the drill string. This fluid removes the cuttings from the hole, can provide a hydrostatic head which controls the formation fluids, and provides cooling for the bit.
Measurement-while-drilling (MWD) systems generally comprise a plurality of sensors disposed in drill collars of a drill string. When the drill string is rotated, the sensors, whether providing focused measurements (e.g., neutron porosity or gamma ray density) or general measurements, measure the formation from all angular directions.
However, when downhole motors are employed to turn the drill bit, the drill string does not rotate. This poses a problem for sensors that are direction sensitive (i.e., provide focused measurements). When the focused sensors are located in different drill collars, the sensors generally measure the formation from different angular directions. The information collected from the several sensors is best interrupted when the formation measurements originate from the same general angular direction. The prior art has addressed this problem by employing spacers or shims between adjacent drill collars having sensors mounted therein (i.e., subs), to provide angular alignment of the sensors. However, the use of shims can be undesirable because of difficulties associated with spacing tapered threads and installation on the rig floor.